Driving device, image reading apparatus and image forming apparatus

ABSTRACT

A driving device is used in an image reading apparatus, and reciprocates a scanning unit for reading an image on an original. The driving device comprises a pull member, a driving pulley which transmits driving force to the pull member, a following pulley which applies tension to the pull member and a pulley holder having a pulley axis which holds the following pulley rotatably. Then, the pulley axis has a lock pawl capable of locking an upper end portion of the following pulley and canceling engagement with the following pulley by being tilted toward a side of an axial center by elastic deformation. Furthermore, the lock pawl is arranged at a side of a tension acting direction from the pull member to the following pulley except the farthest position from the driving pulley among positions in a circumferential direction of the pulley axis. It is possible to attach and detach the following pulley easily at a time of maintenance or the like.

CROSS REFERENCE OF RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2014-022999 filed onFeb. 10, 2014 is incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a driving device, an image readingapparatus and an image forming apparatus, and more specifically, adriving device which reciprocates a scanning unit for reading an imageon an original put on an original platen, an image reading apparatus andan image forming apparatus each provided with the driving device.

2. Description of related art

An example of an image reading apparatus which is provided with such akind of conventional driving device is disclosed in Japanese PatentApplication Laying-open No. H11-215320 [H04N 1/04, G03B 27/50] (PatentLiterature 1) laid-open on Aug. 6, 1999. The driving device of PatentLiterature 1 comprises a transmission timing belt (pull member) fortransmitting driving force of a driving pulley to a reading unit(scanning unit) for reading image information and a tension pulley(following pulley) for applying tension to the transmission timing belt.Then, the tension pulley is supported rotatably by a tension pulleystand (pulley holder) which is fixed to a guide rail.

However, when assembling the driving device of Patent Literature 1,since the following pulley is fixed to the pulley holder with screws orthe like, and the pulley holder is secured to the guide rail with screwsor the like while giving tension to the pull member, a fastening work(assembling work) of the screws is troublesome. Furthermore, when thefollowing pulley is to be exchanged, similarly, a work for removing andfastening of screws is required, and therefore, an exchanging work ofthe following pulley takes time and effort.

SUMMARY OF THE INVENTION

Therefore, it is a primary object of the present invention to provide anovel driving device, image reading apparatus and image formingapparatus.

It is another object of the present invention to provide a drivingdevice, image reading apparatus and image forming apparatus, capable ofattaching or detaching a following pulley easily to or from a pulleyholder.

The present invention adopts the following structure in order to solvethe above-mentioned problem.

A first invention is a driving device that is used in an image readingapparatus and reciprocates a scanning unit for reading an image on anoriginal put on an original platen, comprising: a pull member that pullsthe scanning unit; a driving pulley that transmits driving force to thepull member; a following pulley that the pull member is wound thereonwhile keeping a state where tension is applied to the pull member; and apulley holder having a pulley axis that holds the following pulleyrotatably, wherein the pulley axis has a lock pawl that can lock anupper end portion of the following pulley and cancel engagement with thefollowing pulley by being tilted toward a side of an axial center of thepulley axis by elastic deformation, and the lock pawl is arranged at aside of a tension acting direction from the pull member to the followingpulley except a farthest position from the driving pulley amongpositions in a circumferential direction of the pulley axis.

According to the first invention, since there is provided on the pulleyaxis with the lock pawl capable of locking the upper end portion of thefollowing pulley and canceling the engagement with the following pulleyby being tilted toward the side of the axial center by elasticdeformation, it is possible to make the pulley holder hold the followingpulley rotatably while being retained only by fitting the followingpulley onto the pulley axis. Furthermore, only by pulling the followingpulley out of the pulley axis while tilting the lock pawl to the side ofthe axial center, the following pulley can be removed from the pulleyholder. That is, it is possible to attach or detach the following pulleyeasily to or from the pulley holder.

Furthermore, since screws and washers are not needed when attaching thefollowing pulley to the pulley axis, it is possible to reduce the numberof components and thus a manufacturing cost.

Furthermore, since the lock pawl is arranged at the side of the tensionacting direction from the pull member to the following pulley except thefarthest position from the driving pulley, the lock pawl is hard to bedisengaged from the upper end portion of the following pulley even in astate where the tension is being applied to the pull member.

A second invention is the driving device according to the firstinvention, further comprising a fixing member that fixes the pulleyholder within the image reading apparatus, which being arranged at theside of the tension acting direction from the pull member to thefollowing pulley from the pulley axis.

According to the second invention, since the fixing member is arrangedat the side of the tension acting direction by the pull member from thepulley axis, it becomes possible to arrange the pulley axis and thefollowing pulley near a side plate of a housing of the image readingapparatus, and therefore, miniaturization of the image reading apparatusin a sub-scanning direction is enabled.

A third invention is the driving device according to the firstinvention, wherein the lock pawl is arranged at a position in the sideof the tension acting direction and to a line orthogonally intersectinga line passing the axial center of the pulley axis and extending towardthe tension acting direction with a center line that is a line extendingfrom the axial center of the pulley axis toward the tension actingdirection.

According to the third invention, even in a state where the tension isbeing applied to the pull member, the lock pawl becomes hard to bedisengaged from the upper end portion of the following pulley.

A fourth invention is the driving device according to the firstinvention, wherein the pulley axis has one of the lock pawl that isarranged on a line extending from the axial center of the pulley axis tothe tension acting direction.

According to the fourth invention, since the lock pawl is arranged at aposition that is hardest to receive a load from the pull member, thelock pawl becomes hard to be disengaged from the upper end portion ofthe following pulley. Therefore, the pulley axis can hold the followingpulley more stably.

A fifth invention is the driving device according to the fourthinvention, further comprising a fixing member that fixes the pulleyholder within the image reading apparatus, wherein an axial center ofthe driving pulley, an axial center of the following pulley (that is,the axial center of a pulley axis), a center of the lock pawl and acenter of the fixing member are arranged on a straight line.

A sixth invention is the driving device according to the firstinvention, wherein the pulley axis has two lock pawls arranged in linesymmetry with a center line that is a line passing the axial center ofthe pulley axis and extending toward the tension acting direction.

According to the sixth invention, since the pulley axis has the two lockpawls, it is possible to retain the following pulley more surely.Furthermore, since the two lock pawls are arranged in line symmetry, thepulley axis can rotate the following pulley with well balance.

A seventh invention is the driving device according to the firstinvention, wherein an upper end surface of the lock pawl is made into aflat surface expanding in a direction orthogonally intersecting theaxial center of the pulley axis.

According to the seventh invention, by making the upper end surface ofthe lock pawl into a flat surface, it is possible to make a height sizeof the lock pawl low and thus attain thinning of the pulley holder.

An eighth invention is the driving device according to the firstinvention, wherein an inclined surface that gets down toward the axialcenter of the pulley axis is formed at a side of the axial center of thepulley axis in an upper end portion of the lock pawl.

According to the eighth invention, it becomes possible to largely tiltthe lock pawl toward the side of the axial center of the pulley axiswhen attaching or detaching the following pulley, and therefore, it ispossible to make an engagement amount of the lock pawl with thefollowing pulley larger only by just that much, and accordingly, thefollowing pulley can be retained more surely by the lock pawl.

A ninth invention is an image reading apparatus comprising the drivingdevice according to the first invention.

According to the ninth invention, like the first invention, it ispossible to easily attach or detach the following pulley to or from thepulley holder while the number of components is reducible. Furthermore,the lock pawl is hard to be disengaged from the upper end portion of thefollowing pulley even in a state where the tension is being applied tothe pull member.

A tenth invention is an image forming apparatus comprising the imagereading apparatus according to the ninth invention.

According to the tenth invention, like the ninth invention, it ispossible to easily attach or detach the following pulley to or from thepulley holder while the number of components is reducible. Furthermore,the lock pawl is hard to be disengaged from the upper end portion of thefollowing pulley even in a state where the tension is being applied tothe pull member.

The above described objects and other objects, features, aspects andadvantages of the present invention will become more apparent from thefollowing detailed description of the present invention when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an appearance of an image formingapparatus comprising an image reading apparatus which is a firstembodiment according to the present invention.

FIG. 2 is a plan view showing internal structure of the image readingapparatus of FIG. 1.

FIG. 3 is a sectional view schematically showing a vertical section ofthe image reading apparatus of FIG. 1.

FIG. 4 is a partly enlarged perspective view showing structure of a partof a driving device provided on the image reading apparatus of FIG. 1.

FIG. 5 shows a pulley holder provided on the driving device of FIG. 4,wherein FIG. 5( a) is a perspective view of the pulley holder, FIG. 5(b) is a plan view of the pulley holder, and FIG. 5( c) is a side viewthat the pulley holder is viewed from a front side.

FIG. 6 is a schematic view enlarging and showing a tip end portion of alock pawl provided on the pulley holder of FIG. 5.

FIG. 7 is a schematic view showing an arrangement position of the lockpawl on a pulley axis.

FIG. 8 shows a pulley holder provided on a driving device of an imagereading apparatus which is a second embodiment according to the presentinvention, wherein

FIG. 8( a) is a perspective view of the pulley holder, FIG. 8( b) is aplan view of the pulley holder, and FIG. 8( c) is a side view that thepulley holder is viewed from a rear side.

FIG. 9 shows a pulley holder provided on a driving device of an imagereading apparatus which is a third embodiment according to the presentinvention, wherein

FIG. 9( a) is a perspective view of the pulley holder, FIG. 9( b) is aplan view of the pulley holder, and FIG. 9( c) is a side view that thepulley holder is viewed from a front side.

DETAILED DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS FirstEmbodiment

In the following, an image reading apparatus 100 which is the firstembodiment according to the present invention will be described. FIG. 1is a schematic view showing an appearance of an image forming apparatus102 which comprises the image reading apparatus 100. Furthermore, FIG. 2is a plan view showing internal structure of the image reading apparatus100, and FIG. 3 is a sectional view schematically showing a verticalsection of the image reading apparatus 100.

With reference to FIG. 1-FIG. 3, the image reading apparatus 100comprises a driving device 10 for reciprocating a scanning unit 32 in asub-scanning direction, and is used in the image forming apparatuses 102such as a copying machine, a facsimile, a printer, a multifunctionmachine compounding these, etc. In this embodiment, the image formingapparatus 102 is an MFP (Multifunction Peripheral) which has a copyfunction, a printer function, a scanner function, a facsimile function,etc.

First, fundamental structure of the image forming apparatus 102 will beschematically described. As shown in FIG. 1-FIG. 3, the image formingapparatus 102 comprises a main body 12 and the image reading apparatus100 which is arranged above the main body 12, and forms a multicolor ormonochromatic image onto a predetermined paper (recording paper) basedon image data which is read by the image reading apparatus 100 or imagedata which is sent from an external computer.

A control portion 14 which controls operations of respective parts ofthe image forming apparatus 102 is provided at a predetermined positionwithin the main body 12. The control portion 14 comprises a CPU, amemory, etc., and sends control signals to the respective parts of theimage forming apparatus 102 according to an input operation to anoperating portion 16 such as a touch panel, an operation button, etc.thereby to make the image forming apparatus 102 perform variousoperations.

Furthermore, an image forming portion 18 which comprises an exposureunit, a photoreceptor drum, a charger, a developing device, a fixingroller, etc. are incorporated within the main body 12. The image formingportion 18 forms an image onto the recording paper which is conveyedfrom a paper feed cassette 20 or the like, and discharges animage-formed recording paper on a discharge tray 22.

The image reading apparatus 100 comprises a housing 24 having arectangular plate-like bottom plate 24 a and side walls 24 b which risefrom its peripheral edge portion. There is provided on a top surface ofthe housing 24 with an original platen 26 which is formed of transparentmaterial. Furthermore, an original platen cover 28 is attached on theoriginal platen 26 in an openable and closeable manner via a hinge orthe like. This original platen cover 28 is provided with an ADF(automatic document feeder) 30 which automatically feeds an original puton an original tray to an image reading position one by one.Furthermore, on a front side of the housing 24, there is provided withthe operating portion 16 such as a touch panel, an operation button,etc. which receive an input operation by a user.

Furthermore, within the housing 24, there are provided with a CIS(Contact Image Sensor) scanning body 32 for reading an image on theoriginal put on the original platen 26, a guide shaft 34, the drivingdevice 10 for reciprocating the CIS scanning body 32 under the originalplaten 26, etc. As described later, when an image on the original put onthe original platen 26 is to be read, the CIS scanning body 32reciprocates under the original platen 26, thereby to read the image onthe original to acquire image data thereof. On the other hand, when animage on the original put on an original tray is to be read, the CISscanning body 32 is made to wait under a predetermined image readingposition, and reads the image on the original when the original fed bythe ADF 30 passes through the image reading position (above the CISscanning body 32) to acquire image data.

The CIS scanning body (scanning unit) 32 is an image sensor of aso-called contact type image sensor, and comprises a light source, a rodlens array, a plurality of image sensors (photoelectric conversionelements), etc. The light source is an LED array that a plurality ofLEDs are arranged, for example, and irradiates a surface of theoriginal. The rod lens array makes a reflected light from the originalfocus onto the plurality of image sensors. The plurality of imagesensors read pixel information focused by the rod lens array. Inaddition, it is possible to use a scanning unit using a CCD (ChargeCoupled Device) sensor instead of the CIS scanning body 32.

The guide shaft 34 guides reciprocation of the CIS scanning body 32,which extends in a moving direction (a sub-scanning direction) of theCIS scanning body 32 on the bottom plate 24 a of the housing 24. The CISscanning body 32 is supported by this guide shaft 34 movably, andreciprocates under the original platen 26 by obtaining driving forcefrom the driving device 10.

Subsequently, with reference to FIG. 2-FIG. 6, structure of the drivingdevice 10 will be specifically described. As shown in FIG. 2 and FIG. 3,the driving device 10 comprises a driving pulley 36, a following pulley38, a pull member 40, etc.

The driving pulley 36 is provided near one end portion of the guideshaft 34, and the following pulley 38 is provided near the other endportion of the guide shaft 34. An endless belt-like pull member 40 iswound on (built over) the driving pulley 36 and the following pulley 38,and the CIS scanning body 32 is connected to the pull member 40. Thedriving pulley 36 is rotated by a motor which is a driving source, andtransmits driving force to the pull member 40. The pull member 40 isconstructed by a timing belt, a wire, a chain or the like, and pulls theCIS scanning body 32 by performing circulation movement with rotation ofthe driving pulley 36. Accordingly, the CIS scanning body 32 isreciprocated along with the guide shaft 34. Furthermore, the followingpulley 38 applies predetermined tension to the pull member 40, androtates with the circulation movement of the pull member 40.

In the following, support structure of the following pulley 38 will bedescribed. FIG. 4 is a partly enlarged perspective view showingstructure of a part of the driving device 10 (peripheral part of thefollowing pulley 38) which is provided on the image reading apparatus100. FIG. 5 shows a pulley holder 42 which is provided on the drivingdevice 10, wherein FIG. 5( a) is a perspective view of the pulley holder42, FIG. 5( b) is a plan view of the pulley holder 42, and FIG. 5( c) isa side view that the pulley holder 42 is viewed from the front side.FIG. 6 is a partly sectional view enlarging and showing a tip endportion of a lock pawl 56 which is provided on the pulley holder 42.FIG. 7 is a schematic view showing an arrangement position of the lockpawl 56 on a pulley axis 44.

As shown in FIG. 4, the following pulley 38 is attached to the bottomplate 24 a of the housing 24 using the pulley holder 42. Specifically,the pulley holder 42 is attached to the bottom plate 24 a by a fixingmember 46 such as washers and step screws in a state where the followingpulley 38 is rotatably supported by the pulley axis 44 which is formedon the pulley holder 42. In addition, the pulley holder 42 is madeslidable in the sub-scanning direction by being fitted into a guideportion 48 which projects from the bottom plate 24 a in an approximatelyU-letter shape. Furthermore, a tension applying member 50 which is anelastic member such as a spring is provided in an end portion at a sideof the driving pulley 36 of the pulley holder 42. The pulley holder 42is pushed and energized by this tension applying member 50 in adirection that tension is applied to the pull member 40, i.e., adirection that the following pulley 38 is separated from the drivingpulley 36 along with the guide shaft 34.

Subsequently, specific structure of the pulley holder 42 will bedescribed. As shown in FIG. 5, the pulley holder 42 includes a holdermain body 52, a spring mounting portion 54, a pulley axis 44 having thelock pawl 56, etc., and these are integrally molded by a synthetic resinor the like.

The holder main body 52 is formed in a shape of a rectangular plate, andthe spring mounting portion 54 having a short cylinder shape is formedon an end surface at a side of the driving pulley 36 (that is, a side ofa direction that the following pulley 38 is pulled by the pull member40). In addition, in this first embodiment, the side of the directionthat the following pulley 38 is pulled by the pull member 40 is called aside of a tension acting direction from the pull member 40 to thefollowing pulley 38. The above-mentioned tension applying member 50 isattached to the spring mounting portion 54. Furthermore, the pulley axis44 is formed an end of the holder main body 52 opposite to the springmounting portion 54 to be projected upward. Specific structure of thepulley axis 44 will be described later.

Furthermore, a long hole 60 is formed in a central portion of the holdermain body 52 so as to make the pulley holder 42 adjustable in itsposition in the sub-scanning direction. Then, the above-mentioned fixingmember 46 is fixed to the bottom plate 24 a through this long hole 60.That is, the fixing member 46 for attaching the pulley holder 42 withinthe housing 24 of the image reading apparatus 100 is arranged at a sideof the driving pulley 36 (a side of the tension acting direction fromthe pull member 40 to the following pulley 38) from the pulley axis 44which supports the following pulley 38. Specifically, in thisembodiment, the fixing member 46 is arranged on a line L extending froman axial center C of the pulley axis 44 in the tension acting directionby the pull member 40 (the axial center C and the line L are in FIG. 7).By thus arranging the fixing member 46 at the side of the tension actingdirection by the pull member 40 from the pulley axis 44, the pulley axis44 and the following pulley 38 can be arranged near the side plate 24 bof the housing 24, and therefore, the miniaturization in thesub-scanning direction of the image reading apparatus 100 can beachieved.

Furthermore, projections 62 each having an approximately hemisphereshape in cross-section are formed on both side surfaces of the holdermain body 52 (both end surfaces in a direction orthogonally intersectingthe tension acting direction by the pull member 40). Since tip endportions of these projections 62 are brought into contact with theabove-mentioned guide portion 48, a contacting area between the holdermain body 52 and the guide portion 48 becomes small, and therefore,frictional force between the holder main body 52 and the guide portion48 can be reduced. Therefore, the pulley holder 42 becomes slidablesmoothly within the guide portion 48.

Next, specific structure of the pulley axis 44 will be described. Asshown in FIG. 5, the pulley axis 44 is a spindle which supports thefollowing pulley 38 rotatably, and comprises a shaft main body 64 whichis formed in an approximately cylindrical shape. An outer diameter ofthe shaft main body 64 is approximately the same as an inner diameter ofthe following pulley 38, and the following pulley 38 rotates in a mannerthat an inner side surface of the following pulley 38 is slid on anouter side surface of the shaft main body 64. Furthermore, a part in acircumferential direction of the shaft main body 64 is notched, and thelock pawl 56 for locking an upper end portion of the following pulley 38is formed in such a notched portion. In this first embodiment, a singlelock pawl 56 is arranged at a side of the tension acting direction fromthe pull member 40 to the following pulley 38 among circumferentialpositions of the pulley axis 44. Specifically, the lock pawl 56 isarranged at a position nearest to the driving pulley 36 on a linepassing an axial center C of the pulley axis 44 and extending in thetension acting direction by the pull member 40. That is, in thisembodiment, the axial center of the driving pulley 36, the axial centerof the following pulley 38 (that is, the axial center C of the pulleyaxis 44), the center of the lock pawl 56 and the center of the fixingmember 46 are arranged on a straight line (see FIG. 2).

The lock pawl 56 includes a tiltable piece 56 a which projects outwardlyfrom an inner surface of the shaft main body 64 and stands upwardly anda locking piece 56 b which extends outwardly from a tip end portion ofthe tiltable piece 56 a. When the upper end portion of the followingpulley 38 is locked by this locking piece 56 b, the following pulley 38which is held rotatably by the pulley axis 44 can be retained (see FIG.4 and FIG. 6). Furthermore, a width size in a radial direction of thepulley axis 44 of the tiltable piece 56 a is formed to be smaller than awidth size in a circumferential direction of the pulley axis 44. Thatis, the tiltable piece 56 a (lock pawl 56) is formed in a shape that ishard to tilt to a side of the circumferential direction of the pulleyaxis 44, but easy to tilt toward a side of the axial center C of thepulley axis 44. The lock pawl 56 can cancel engagement with thefollowing pulley 38 by tiling toward the side of the axial center C ofthe pulley axis 44 by elastic deformation. Furthermore, a plate-likereinforcement portion 66 is integrally formed on a lower end portion ofthe lock pawl 56.

Furthermore, as shown well in FIG. 6, a straight line-like inclinedsurface 56 c which gets down outwardly is formed at an outer side in theupper end portion (an upper surface of the tip end portion) of the lockpawl 56. By forming the inclined surface 56 c, in attaching thefollowing pulley 38 to the pulley axis 44, the lock pawl 56 becomes tonaturally tilt toward the side of the axial center C of the pulley axis44 because the lower end portion of the pulley axis 44 abuts on theinclined surface 56 c. Therefore, attachment of the following pulley 38becomes easy.

Furthermore, the upper end surface of the lock pawl 56 is made into aflat surface 56 d which expands in a direction orthogonally intersectingthe axial center C of the pulley axis 44. By making the upper endsurface of the lock pawl 56 into the flat surface 56 d, it is possibleto make a height size of the lock pawl 56 low and thus attain thinningof the pulley holder 42.

Furthermore, a circular arc-like (rounded shape) inclined surface 56 ewhich gets down toward the axial center C of the pulley axis 44 isformed at a side of the axial center C in the upper end portion of thelock pawl 56. By forming the inclined surface 56 e, in attaching ordetaching the following pulley 38, it is possible to largely tilt thelock pawl 56 toward the side of the axial center C of the pulley axis44. That is, although the upper end portion largely falls down becausethe upper end portion of the lock pawl 56 is tilted with a fulcrum inits lower end portion, by forming the inclined surface 56 e at a side ofthe shape center C in the upper end portion of the lock pawl 56, thatis, by not forming an edge portion, the lock pawl 56 becomes hard tointerfere with the shaft main body 64 if the lock pawl 56 is largelytilted. If the lock pawl 56 is largely tilted toward the side of theaxial center C of the pulley axis 44, it is possible to make anengagement amount (engagement length) of the lock pawl 56 to thefollowing pulley 38 larger only by just that much, and therefore, itbecomes possible to retain the following pulley 38 more surely by thelock pawl 56. An advantage according to formation of the inclinedsurface 56 e is especially demonstrated remarkably in a case where aplurality of lock pawls 56 are formed on the pulley axis 44 like a thirdembodiment describe later. This is because it is possible to preventeach of the lock pawls 56 from interfering with each other even iftilting.

In addition, in the first embodiment, the inclined surface 56 c is madeinto a straight line-like inclined surface, and the inclined surface 56e is made into a circular arc-like inclined surface. However, theinclined surface 56 c may be made into a circular arc-like inclinedsurface, and the inclined surface 56 e may be made into a straightline-like inclined surface.

Here, it is preferable that an arrangement position of the lock pawl 56in a circumferential direction of the pulley axis 44 is at a side of adirection that the following pulley 38 is pulled by the pull member 40,i.e., a side of a tension acting direction (see FIG. 7) except afarthest position from the driving pulley 36. This is because there is apossibility that the lock pawl 56 may be disengaged due to a load fromthe pull member 40 if the lock pawl 56 is arranged at a side opposite tothe side of the tension acting direction from the pull member 40 to thefollowing pulley 38. That is, the following pulley 38 is pulled by thepull member 40 in a state where the tension is applied to the pullmember 40. If the lock pawl 56 is arranged at a side opposite to theside of the tension acting direction from the pull member 40 to thefollowing pulley 38, the lock pawl 56 is bent toward a side of the axialcenter C of the pulley axis 44 due to the load from the pull member 40because the lock pawl 56 is formed to be tiltable (easy to bend) towardthe side of the axial center C of the pulley axis 44. If this bendbecomes large, the following pulley 38 becomes in a condition to runonto a tip end of the lock pawl 56, and therefore, the engagement of thefollowing pulley 38 by the lock pawl 56 comes to be disengaged.Accordingly, since the following pulley 38 becomes to rotate in a statewhere the tip end of the lock pawl 56 and the following pulley 38 arebrought into contact with each other, a rotation load of the followingpulley 38 becomes large. In addition to this, there is also apossibility of leading to breakage of the pulley axis 44 and thefollowing pulley 38. Therefore, it is preferable that the lock pawl 56is arranged at the side of the tension acting direction from the pullmember 40 to the following pulley 38 except the farthest position fromthe driving pulley 36 as mentioned above.

In addition, as shown in FIG. 7, in the present invention, it ispossible to say that the side of the tension acting direction indicatingan arrangement position of the lock pawl 56 is a range except adirection that the following pulley 38 applies the tension to the pullmember 40 (a tension applying direction by the following pulley 38).Within such a range, preferably, the lock pawl 56 is arranged in a rangeR of 270 degrees with a center line (center) that is a line L extendingtoward the tension acting direction from the axial center C of thepulley axis 44 among circumferential positions of the pulley axis 44,that is, in a range R of 270 degrees between two lines each having anangle of 135 degrees in a clockwise rotation and a counterclockwiserotation against the line L extending toward the tension actingdirection from the axial center C at the side of the tension actingdirection (side of the driving pulley 36). More preferably, the lockpawl 56 is arranged at a position (range) defined by a line orthogonallyintersecting a line passing the axial center C of the pulley axis 44 andextending toward the tension acting direction with a center line that isthe line L extending from the axial center C of the pulley axis 44toward the tension acting direction at the side of the tension actingdirection (side of the driving pulley 36). Most preferably, the lockpawl 56 is arranged at a position that is hardest to receive the loadfrom the pull member 40, and specifically, at a position on the line Lextending from the axial center C of the pulley axis 44 toward thetension acting direction by the pull member 40, that is, a positionnearest the driving pulley 36 as shown in FIG. 5.

In the pulley holder 42 having the pulley axis 44 of such structure,only by fitting the following pulley 38 onto the pulley axis 44 as thefollowing pulley 38 is pushed from the top, the following pulley 38 canbe attached to the pulley axis 44. In a state where the following pulley38 is attached to the pulley axis 44, i.e., at a time of use, since theupper end portion of the following pulley 38 is locked by the lockingpiece 56 b of the lock pawl 56, the following pulley 38 can be surelyretained. Furthermore, at a time of exchange or maintenance of the pullmember 40, the following pulley 38, etc., the following pulley 38 can bedetached from the pulley axis 44 only by pulling out the followingpulley 38 while tilting the lock pawl 56 toward the side of the axialcenter C by elastic deformation.

According to this first embodiment, the lock pawl 56 which can lock theupper end portion of the following pulley 38 and cancel the engagementwith the following pulley 38 by tilting toward the side of the axialcenter C by elastic deformation is provided on the pulley axis 44 whichis provided on the pulley holder 42. Therefore, only by fitting thefollowing pulley 38 onto the pulley axis 44, it is possible to hold thefollowing pulley 38 on the pulley holder 42 (pulley axis 44) in a statewhere the following pulley 38 can be rotated and retained. That is, anattachment work of the following pulley 38 to the pulley holder 42becomes easy. Furthermore, since what is necessary is just to pull outthe following pulley 38 from the pulley axis 44 while the lock pawl 56is tilted toward the side of the axial center C when removing thefollowing pulley 38, a removal work of the following pulley 38 alsobecomes easy. That is, according to the first embodiment, it is possibleto attach and detach the following pulley 38 easily to or from thepulley holder 42.

Furthermore, according to the first embodiment, since attachment memberssuch as screws and washers are not needed when attaching the followingpulley 38 to the pulley axis 44, it is possible to reduce the number ofcomponents and thus a manufacturing cost.

Furthermore, according to the first embodiment, since the lock pawl 56is arranged at the side of the tension acting direction from the pullmember 40 to the following pulley 38 except the farthest position fromthe driving pulley 36, even in a state where the tension is applied tothe pull member 40, the lock pawl 56 is hard to be disengaged from theupper end portion of the following pulley 38. In particular, in thisfirst embodiment, since the lock pawl 56 is arranged at a positionnearest to the driving pulley 36, which is hardest to receive a loadfrom the pull member 40, the pulley axis 44 can hold the followingpulley 38 more stably.

Second Embodiment

Next, with reference to FIG. 8, an image reading apparatus 100 which isthe second embodiment of according to the present invention. In thissecond embodiment, an arrangement position of the lock pawl 56 differsfrom those of the above-mentioned first embodiment. Since structure ofother portions is not changed, by applying the same reference numeralsto portions which are common in the above-mentioned first embodiment, aduplicate description is omitted or simplified. Then, in the following,only the structure of a pulley holder 42 which is provided on thedriving device 10 of the image reading apparatus 100 of this secondembodiment will be described. FIG. 8 shows a pulley holder 42 which isprovided on the driving device 10 of an image reading apparatus 100,wherein FIG. 8( a) is a perspective view of the pulley holder 42, FIG.8( b) is a plan view of the pulley holder 42, and FIG. 8( c) is a sideview that the pulley holder 42 is viewed from a rear side.

As shown in FIG. 8, the pulley holder 42 includes the holder main body52, the spring mounting portion 54, the pulley axis 44 having the lockpawl 56, etc., and these are integrally molded by a synthetic resin orthe like. The lock pawl 56 includes the tiltable piece 56 a and thelocking piece 56 b, a width size of the tiltable piece 56 a in a radialdirection of the pulley axis 44 is formed smaller than a width size in acircumferential direction of the pulley axis 44.

Then, in the second embodiment, the lock pawl 56 is arranged on a lineorthogonally intersecting a line passing the axial center C of thepulley axis 44 and extending in the tension acting direction amongcircumferential positions of the pulley axis 44. If the lock pawl 56 isarranged at such a position, since a load from the pull member 40 ismainly applied to the shaft main body 64 in a state where the tension isapplied to the pull member 40, the load that is applied to the lock pawl56 becomes small. Furthermore, since the lock pawl 56 is formed in ashape that is hard to be tilted to a side of the circumferentialdirection of the pulley axis 44, even if the lock pawl 56 receives aload from the pull member 40, the lock pawl 56 is hard to be bent in thetension acting direction. Therefore, the lock pawl 56 is hard to bedisengaged from the upper end portion of the following pulley 38, andthe pulley axis 44 can hold the following pulley 38 stably.

According to this second embodiment, since the pulley axis 44 has thelock pawl 56, like the above-mentioned first embodiment, it is possibleto easily attach and detach the following pulley 38 to or from thepulley holder 42.

Furthermore, according to the second embodiment, since the lock pawl 56is arranged at the side of the tension acting direction from the pullmember 40 to the following pulley 38 except the farthest position fromthe driving pulley 36, the lock pawl 56 is hard to be disengaged fromthe upper end portion of the following pulley 38 even in a state wherethe tension is applied to the pull member 40.

In addition, in the second embodiment, although the lock pawl 56 isarranged to a rear side in FIG. 8, of course, the lock pawl 56 may bearranged an opposite side, i.e., a front side.

Third Embodiment

Subsequently, with reference to FIG. 9, an image reading apparatus 100which is the third embodiment according to the present invention. Thisthird embodiment is different from the above-mentioned first and secondembodiments in a point which two lock pawls 56 are formed on the pulleyaxis 44. Since structure of other portions is not changed, by applyingthe same reference numerals to portions which are common in theabove-mentioned first and second embodiments, a duplicate description isomitted or simplified. Then, in the following, only structure of apulley holder 42 which is provided on the driving device 10 of the imagereading apparatus 100 of this third embodiment. FIG. 9 shows the pulleyholder 42 which is provided on the driving device 10 of the imagereading apparatus 100, wherein FIG. 9( a) is a perspective view of thepulley holder 42, FIG. 9( b) is a plan view of the pulley holder 42, andFIG. 9( c) is a side view that the pulley holder 42 is viewed from afront side.

As shown in FIG. 9, the pulley holder 42 includes the holder main body52, the spring mounting portion 54, the pulley axis 44 having the lockpawls 56, etc., and these are integrally molded by a synthetic resin orthe like.

The pulley axis 44 comprises the shaft main body 64 which is formed in ashape of an approximately cylinder-like. The shaft main body 64 isnotched in two places on a line orthogonally intersecting a line passingthe axial center C of the pulley axis 44 and extending in the tensionacting direction, and the lock pawl 56 is formed in each of notchedportions. That is, in this third embodiment, the pulley axis 44 has thetwo lock pawls 56, and the two lock pawls 56 are arranged in linesymmetry with a center line that is a line passing the axial center C ofthe pulley axis 44 and extending in the tension acting direction.

The lock pawl 56 includes the tiltable piece 56 a which is a rectangularplate-like and protrudes upward from the holder main body 52 and alocking piece 56 b extending outwardly from the tip end portion of thetiltable piece 56 a. Then, a width size of the tiltable piece 56 a in aradial direction of the pulley axis 44 is formed smaller than a widthsize in a circumferential direction of the pulley axis 44. Furthermore,a circular arc-like inclined surface 56 e which gets down toward theaxial center C of the pulley axis 44 is formed at a side of the axialcenter C in the upper end portion of the lock pawl 56 (see FIG. 6). In acase of the two lock pawls 56, at a time of attaching or detaching thefollowing pulley 38, each of the two lock pawls 56 is tilted toward theside of the axial center C, but because the inclined surface 56 e isformed at the side of the axial center C in the upper end portion of thelock pawl 56, the lock pawls 56 become hard to interfere with eachother.

According to this third embodiment, since the pulley axis 44 has thelock pawls 56, like the above-mentioned first embodiment, it is possibleto easily attach and detach the following pulley 38 to or from thepulley holder 42.

Furthermore, according to the third embodiment, since the lock pawls 56are arranged at a side of the tension acting direction from the pullmember 40 to the following pulley 38 except the farthest position fromthe driving pulley 36, the lock pawls 56 are hard to be disengaged fromthe upper end portion of the following pulley 38 even in a state wherethe tension is applied to the pull member 40.

Furthermore, according to the third embodiment, since the pulley axis 44has the two lock pawls 56, it is possible to retain the following pulley38 more surely.

Furthermore, since the two lock pawls 56 are arranged in line symmetrywith a center line that is a line passing the axial center C of thepulley axis 44 and extending in the tension acting direction, the pulleyaxis 44 can rotate the following pulley 38 with well balance.

In addition, a specific shape of the lock pawl 56 is not limited to theshape as shown in the first to third embodiments, and a proper shape isemployable if it is a shape capable of locking the upper end portion ofthe following pulley 38 and capable of canceling the engagement with thefollowing pulley 38 by being tilted toward the side of the axial centerC by elastic deformation.

Furthermore, in each of the above-mentioned first to third embodiments,although the driving device 10 is applied to the image forming apparatus(multifunction machine) 102 that the image reading apparatus 100 and themain body 12 comprising the image forming portion 18 are integrated, notlimited to this. For example, the image reading apparatus 100 comprisingthe driving device 10 may be an individual product. That is, the drivingdevice 10 may be applied to the image reading apparatus 100 which hasonly a scanner function. In this case, the image reading apparatus 100is connected to a network and transmits a read image to a personalcomputer, other image forming apparatuses, etc., for example.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

What is claimed is:
 1. A driving device that is used in an image readingapparatus and reciprocates a scanning unit for reading an image on anoriginal put on an original platen, comprising: a pull member that pullsthe scanning unit; a driving pulley that transmits driving force to thepull member; a following pulley that the pull member is wound thereonwhile keeping a state where tension is applied to the pull member; and apulley holder having a pulley axis that holds the following pulleyrotatably, wherein the pulley axis has a lock pawl that can lock anupper end portion of the following pulley and cancel engagement with thefollowing pulley by being tilted toward a side of an axial center of thepulley axis by elastic deformation, and the lock pawl is arranged at aside of a tension acting direction from the pull member to the followingpulley except a farthest position from the driving pulley amongpositions in a circumferential direction of the pulley axis.
 2. Thedriving device according to claim 1, further comprising a fixing memberthat fixes the pulley holder within the image reading apparatus, whichbeing arranged at the side of the tension acting direction from the pullmember to the following pulley from the pulley axis.
 3. The drivingdevice according to claim 1, wherein the lock pawl is arranged at aposition in the side of the tension acting direction and to a lineorthogonally intersecting a line passing the axial center of the pulleyaxis and extending toward the tension acting direction with a centerline that is a line extending from the axial center of the pulley axistoward the tension acting direction.
 4. The driving device according toclaim 1, wherein the pulley axis has one of the lock pawl that isarranged on a line extending from the axial center of the pulley axis tothe tension acting direction.
 5. The driving device according to claim4, further comprising a fixing member that fixes the pulley holderwithin the image reading apparatus, wherein an axial center of thedriving pulley, an axial center of the following pulley, a center of thelock pawl and a center of the fixing member are arranged on a straightline.
 6. The driving device according to claim 1, wherein the pulleyaxis has two lock pawls arranged in line symmetry with a center linethat is a line passing the axial center of the pulley axis and extendingtoward the tension acting direction.
 7. The driving device according toclaim 1, wherein an upper end surface of the lock pawl is made into aflat surface expanding in a direction orthogonally intersecting theaxial center of the pulley axis.
 8. The driving device according toclaim 1, wherein an inclined surface that gets down toward the axialcenter of the pulley axis is formed at a side of the axial center of thepulley axis in an upper end portion of the lock pawl.
 9. An imagereading apparatus comprising the driving device according to claim 1.10. An image forming apparatus comprising the image reading apparatusaccording to claim 9.